The flat panel detection technology has made rapid development in recent years, and can be classified into two types: direct type and indirect type, and the key component of an indirect flat panel detector is a flat panel detector (FPD) for acquiring images. An X-ray flat panel detector includes an array substrate including an X-ray transforming layer, and a thin film transistor and an amorphous silicon photodiode are included in each detection unit of the array substrate. The amorphous silicon photodiode starts to operate under the action of a reversed voltage. When the array substrate is irradiated by an X-ray, the X-ray is converted into a visible light beam by the X-ray transforming layer, then the visible light beam is converted into an electrical signal by the amorphous silicon photodiode, and it is stored. Under the action of a driving circuit, thin film transistors are switched on row by row, charges converted by photodiodes are transmitted to a data processing circuit, and further processes such as amplification, analog/digital conversion, and so on will be carried out by the data processing circuit, so as to ultimately obtain the image information.
An amorphous silicon thin film in an amorphous silicon photodiode suffers from a light-induced degradation effect, and this leads to degradation in the photoelectric conversion efficiency of the photodiode after it is irradiated by light for long time. In order to reduce the occurrence of light-induced degradation phenomenon, thickness of the amorphous silicon thin film can be reduced. But when thickness of the amorphous silicon thin film is reduced, incident lights cannot be fully absorbed, and the following case will occur: a great amount of light is transmitted by a photodiode element, and the conversion efficiency of the photodiode is reduced.